Magnetic resonance projection imaging

ABSTRACT

Apparatus and techniques are described herein for nuclear magnetic resonance (MR) projection imaging. Such projection imaging may be used to control radiation therapy delivery to a subject, such as including receiving reference imaging information, generating a two-dimensional (2D) projection image using imaging information obtained via nuclear magnetic resonance (MR) imaging, the 2D projection image corresponding to a specified projection direction, the specified projection direction including a path traversing at least a portion of an imaging subject, determining a change between the generated 2D projection image and the reference imaging information, and controlling delivery of the radiation therapy at least in part using the determined change between the obtained 2D projection image and the reference imaging information.

CLAIM OF PRIORITY

This application is a continuation of U.S. application Ser. No.15/534,328, filed Jun. 8, 2017, which is a U.S. national stageapplication filed under 35 U.S.C. § 371 from International ApplicationSerial No. PCT/US2015/065014, filed on Dec. 10, 2015, and published asWO 2016/094668 on Jun. 16, 2016, which application claims the benefit ofpriority of Lachaine et al., U.S. Provisional Patent Application Ser.No. 62/090,115 titled “MAGNETIC RESONANCE PROJECTION IMAGING,” filed onDec. 10, 2014, the benefit of priority of each of which is herebypresently claimed, and each of which applications and publication arehereby incorporated by reference herein in their entireties.

BACKGROUND

Radiation therapy or “radiotherapy” may be used to treat cancers orother ailments in mammalian (e.g., human and animal) tissue. One suchradiotherapy technique is referred to as “gamma knife,” by which apatient is irradiated using a number of lower-intensity gamma rays thatconverge with higher intensity and high precision at a targeted region(e.g., a tumor). In another example, radiotherapy is provided using alinear accelerator (“linac”), whereby a targeted region is irradiated byhigh-energy particles (e.g., electrons, protons, ions, high-energyphotons, and the like). The placement and dose of the radiation beam isaccurately controlled to provide a prescribed dose of radiation to thetargeted region. The radiation beam is also generally controlled toreduce or minimize damage to surrounding healthy tissue, such as may bereferred to as “organ(s) at risk” (OARs). Radiation may be referred toas “prescribed” because generally a physician orders a predefined doseof radiation to be delivered to a targeted region such as a tumor.

Generally, ionizing radiation in the form of a collimated beam isdirected from an external radiation source toward a patient. Modulationof a radiation beam may be provided by one or more attenuators orcollimators (e.g., a multi-leaf collimator). The intensity and shape ofthe radiation beam may be adjusted by collimation avoid damaging healthytissue (e.g., OARs) adjacent to the targeted tissue by conforming theprojected beam to a profile of the targeted tissue.

The treatment planning procedure may include using a three-dimensionalimage of the patient to identify the target region (e.g., the tumor) andsuch as to identify critical organs near the tumor. Creation of atreatment plan may be a time consuming process where a planner tries tocomply with various treatment objectives or constraints (e.g., dosevolume histogram (DVH) objectives or other constraints), such as takinginto account importance (e.g., weighting) of respective constraints inorder to produce a treatment plan that is clinically acceptable. Thistask may be a time-consuming trial-and-error process that is complicatedby the various organs at risk (OARs) because as the number of OARsincreases (e.g., about thirteen for a head-and-neck treatment), so doesthe complexity of the process. OARs distant from a tumor may be moreeasily spared from radiation, but OARs close to or overlapping a targettumor may be more difficult to spare from radiation exposure duringtreatment.

Generally, for each patient, an initial treatment plan may be generatedin an “offline” manner. The treatment plan may be developed well beforeradiation therapy is delivered, such as using one or more medicalimaging techniques. Imaging information may include, for example, imagesfrom X-rays, Computed Tomography (CT), nuclear magnetic resonance (MR),positron emission tomography (PET), single-photon emission computedtomography (SPECT), or ultrasound. A health care provider, such as aphysician, may use three-dimensional imaging information indicative ofthe patient anatomy to identify one or more target tumors along with theorgans at risk near the tumor. The health care provider may delineatethe target tumor that is to receive a prescribed radiation dose using amanual technique, and the health care provider may similarly delineatenearby tissue, such as organs, at risk of damage from the radiationtreatment.

Alternatively or additionally, an automated tool (e.g., ABAS provided byElekta AB, Sweden) may be used to assist in identifying or delineatingthe target tumor and organs at risk. A radiation therapy treatment plan(“treatment plan”) may then be created using an optimization techniquebased on clinical and dosimetric objectives and constraints (e.g., themaximum, minimum, and mean doses of radiation to the tumor and criticalorgans).

The treatment planning procedure may include using a three-dimensionalimage of the patient to identify the target region (e.g., the tumor) andto identify critical organs near the tumor. Creation of a treatment planmay be a time consuming process where a planner tries to comply withvarious treatment objectives or constraints (e.g., dose volume histogram(DVH) objectives), taking into account their individual importance(e.g., weighting) in order to produce a treatment plan that isclinically acceptable. This task may be a time-consuming trial-and-errorprocess that is complicated by the various organs at risk (OARs) becauseas the number of OARs increases (e.g., up to thirteen for ahead-and-neck treatment), so does the complexity of the process. OARsdistant from a tumor may be easily spared from radiation, while OARsclose to or overlapping a target tumor may be difficult to spare.

The treatment plan may then be later executed by positioning the patientand delivering the prescribed radiation therapy. The radiation therapytreatment plan may include dose “fractioning,” whereby a sequence ofradiation therapy deliveries are provided over a predetermined period oftime (e.g., 45 fractions or some other total count of fractions), suchas with each therapy delivery including a specified fraction of a totalprescribed dose. During treatment, the position of the patient or theposition of the target region in relation to the treatment beam isimportant because such positioning in part determines whether the targetregion or healthy tissue is irradiated.

OVERVIEW

In one approach, nuclear magnetic resonance (MR) imaging may be combinedwith a radiation therapy system such as to provide imaging informationto adapt or guide radiation therapy. An example of such a combinedsystem may be referred to generally as “MRI-linac,” comprising an MRimaging system, along with linear accelerator as a source of energy forradiation therapy. In an illustrative example, image acquisition may beperformed just before initiation of delivery of a specified radiationtherapy fraction. Such imaging may provide information helpful foridentifying a position of a target region or for identifying motion ofthe target region. Such contemporaneous imaging may be referred togenerically as “real-time,” but in general a latency or time delayexists between an acquisition of an image and a delivery of radiationtherapy.

The present inventors have recognized, among other things, that aproblem exists in using 3D MR imaging to plan or adapt radiationtherapy. For example, image reconstruction of an imaged volumetricregion may be adversely affected when the target region is influenced byrespiration or other motion, because the imaging duration (“imagingtime”) is generally long enough to be affected by such motion. Inaddition, an acquisition latency or a long acquisition duration may beproblematic because the target region may have deformed or movedsignificantly between a 3D MR image acquisition and a later radiationtherapy delivery.

In one approach, such as when target region motion is periodic, afour-dimensional MR imaging technique may be used such as prior toradiation treatment. For example, image acquisition may be synchronizedto a physiologic cycle, such as by sensing surrogate information.Examples of surrogates include a signal sensed using a respiration beltor a one-dimensional (1D) navigator echo indicated by MR imaging. MRimaging elements, such as acquired imaging slices, may be sorted intobins using information indicative of a phase or amplitude of thephysiologic cycle or a surrogate correlated with such a cycle. However,such an approach may also have limitations. For example, generallyavailable slice-based 4D imaging techniques (such as non-projection MRimaging) do not include use of an anatomical landmark such as adiaphragm location to sort or bin acquired 3D images with respect to aphysiologic cycle. Instead, generally available 4D imaging techniquesacquire images sequentially and the acquired images contain differentportions of the anatomy and lack common anatomical features across eachimage. By contrast, a projection imaging approach can include selectingor generating projection images having a common anatomical feature ineach image so the common feature can be used to facilitate binning. Evenif a different perspective of the feature is present in each of theprojection images (e.g., different views of the feature), such featuretracking for binning can still be used in a projection imaging approach.In this manner, unlike generally-available 4D MR imaging techniques, asurrogate (such as an external surrogate) is not required.

Generally-used 4D MR imaging protocols also include relatively longacquisition times and may be time-prohibitive, such as in applicationswhere updated imaging is to be performed prior to each radiation therapytreatment fraction. Also, 4D MR imaging techniques may not necessarilyrepresent or predict an anatomical state of an imaging subject during asubsequent delivery of radiation therapy. For example, baseline drifts,deformations, or changes in frequency or phase of the physiologic cyclemay occur between the time at which the 4D MR imaging information isacquired, and a later delivery of radiation therapy.

In another approach, imaging information indicative of intrafractionalmotion of the target region or other portions of the imaging subject mayinclude imaging just a portion of the imaging subject, without requiringfull volumetric imaging, such as by acquiring two-dimensional (2D)imaging slices, such as through the target region along differentdirections (such as including acquisition of a sequence of orthogonalslices). Such slices may be used to help localize the target region orother anatomy, generally, for delivery of radiation therapy. Suchlocalization may be assisted in part using one or more of imagesegmentation or image registration techniques. However, such an approachmay also have limitations. For example, MR imaging pulse sequences usedto obtain 2D slices may be different than those used to obtainpre-treatment interfractional volumetric 3D or 4D “reference” imaging.Such different pulse sequences may make registration between 2D slicesand an earlier-acquired volumetric reference image challenging. Anotherlimitation is that out-of-slice information is lost, such as in anexample where multiple organs-at-risk (OARs) are present or ifretrospective dose calculations are to be made by acquiring imaginginformation during treatment. Yet another limitation of using 2D imagingslices is that it may be difficult to align slices with target motion,particularly if the motion varies between physiologic cycles such asbetween respiration cycles. Small targets such as tumors may be deformedor may disappear entirely from a particular acquired imaging slice.

The present inventors have recognized a solution to the limitationsmentioned above. Such a solution may include using an MR projectionimaging approach. Such a projection imaging approach may be usedintrafractionally. Alternatively, or additionally, MR projection imagingmay be used in a similar manner for simulation imaging to be used fortreatment planning, or pre-treatment (e.g., “reference”) imagingperformed interfractionally to shift the patient or adapt the treatmentplan prior to treatment delivery. Use of MR projection imaging forsimulation imaging, pre-treatment reference imaging, and laterintrafractional imaging may provide consistency and ease of registrationor other processing. MR projection imaging may also provide imaginginformation in manner that more closely correlates with beam-eye-view(BEV) portal imaging or X-ray techniques, but without exposing theimaging subject to ionizing radiation during imaging. Obtaining 2D MRprojection images may dramatically decrease imaging acquisition latencyas compared to other approaches such as full 3D volumetric MR imaging,and 2D projection images may be aggregated such as to provide volumetricimaging information using tomographic or Fourier domain (k-space)techniques, for example. Information from acquired 2D MR projectionimages or from 3D or 4D imaging constructed from 2D MR projection imagesmay be compared to reference imaging information, such as to localize atarget region or anatomical landmarks, or to predict a later targetregion location. In this manner, information indicative of the targetregion may be used to adapt radiation therapy.

According to various examples, apparatus and techniques described hereinmay be used to control radiation therapy delivery to a subject usingprojection imaging techniques. For example, reference imaging may bereceived, such as including imaging information obtained earlier inrelation to radiation therapy treatment planning. A two-dimensional (2D)projection image may be generated using imaging information obtained vianuclear magnetic resonance (MR) imaging, the 2D projection imagecorresponding to a specified projection direction, the specifiedprojection direction including a path traversing at least a portion ofan imaging subject. A change between the generated 2D projection imageand the reference imaging information may be determined. Delivery of theradiation therapy may be controlled at least in part (e.g., in anadaptive manner) using the determined change between the obtained 2Dprojection image and the reference imaging information.

The present inventors have also recognized that reference imaginginformation may be obtained using projection imaging techniques, such asfor use in spatially-registering later-obtained projection images withearlier-acquired imaging information. According to various examples,apparatus and techniques described herein may be used to generatefour-dimensional (4D) or other imaging information, such as during oneor more of obtaining reference images before radiation therapy (e.g.,reference imaging), or later such as just before or during delivery ofradiation therapy (e.g., intrafractional imaging). Generating the 4Dimaging information may include generating two or more two-dimensional(2D) images, the 2D images comprising projection images representativeof different projection angles, where the 2D images are generated usingimaging information obtained via nuclear magnetic resonance (MR)imaging. Particular 2D images may be assigned to bins at least in partusing information indicative of temporal positions within thephysiologic cycle corresponding to the particular 2D images.Three-dimensional (3D) images may be constructed using the binned 2Dimages. A group of 3D images may be aggregated such as to provide 4Dimaging information.

This overview is intended to provide an overview of subject matter ofthe present patent application. It is not intended to provide anexclusive or exhaustive explanation of the invention. The detaileddescription is included to provide further information about the presentpatent application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates generally an example of a radiation therapy systemthat may include radiation therapy output configured to provide atherapy beam.

FIG. 1B illustrates generally a partially cut-away view of an example ofa system that including a combined radiation therapy system and anuclear magnetic resonance (MR) imaging system.

FIG. 2 illustrates generally an example of a collimator configuration,such as may be used in part to shape or collimate a radiation therapybeam.

FIG. 3 illustrates generally an example of radiation therapy system,such as may include a radiation therapy device and an imagingacquisition device.

FIG. 4 illustrates generally an example of a system that may be used forone or more of imaging acquisition, image segmentation, targetprediction, therapy control, or therapy adjustment.

FIG. 5 illustrates generally an example of a system, such as may includea radiation therapy controller having an imaging input, a radiationtherapy generator, and a radiation therapy output.

FIG. 6 illustrates generally a technique, such as a method, that mayinclude using MR imaging to excite a region of an imaging subject, theregion defining an imaging slice, and obtaining a pixel valuecorresponding to a one-dimensional projection line through the slice.

FIG. 7A illustrates generally a technique, such as a method, that mayinclude exciting a region of an imaging subject using a two-dimensional(2D) MR imaging excitation sequence

FIG. 7B illustrates generally another technique, such as a method, thatmay include exciting a region of an imaging subject using atwo-dimensional (2D) MR imaging excitation sequence.

FIGS. 8A and 8B illustrate generally a technique, such as a method, thatmay include generating two-dimensional (2D) MR projection imagesrepresentative of different projection angles, and using such 2Dprojection images to construct three-dimensional (3D) images.

FIG. 9 illustrates generally a technique, such as a method, that mayinclude generating a two-dimensional (2D) projection image using MRimaging and determining a change between the generated 2D projectionimage and reference imaging information.

FIG. 10A illustrates generally a spatial arrangement of a radiationtherapy beam orientation with respect to one or more projectiondirections, such as may include two projection directions orientedorthogonally to each other.

FIG. 10B illustrates generally a spatial arrangement of MR imagingprojection directions, such as corresponding to projection anglesspanning an arc or circle about a specified region such as a radiationtherapy treatment isocenter.

FIG. 10C illustrates generally a spatial arrangement of an MR imagingprojection direction, such as oriented at a specified angle with respectto a radiation therapy beam direction

FIG. 10D illustrates generally a spatial arrangement of MR imagingprojection directions, such as may be specified to provide MR projectionimages in a manner similar to stereoscopic X-ray imaging.

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

DETAILED DESCRIPTION

FIG. 1A illustrates generally an example of a radiation therapy system102 that may include radiation therapy output 104 configured to providea therapy beam 108. The radiation therapy output 104 may include one ormore attenuators or collimators, such as a multi-leaf collimator (MLC)as described in the illustrative example of FIG. 2. Referring back toFIG. 1A, a patient may be positioned in a region 112, such as on aplatform 116 (e.g., a table or a couch), to receive a prescribedradiation therapy dose according to a radiation therapy treatment plan.

The radiation therapy output 104 may be located on a gantry 106 or othermechanical support, such as to rotate the therapy output 104 around anaxis (“A”). One or more of the platform 116 or the radiation therapyoutput 104 may be moveable to other locations, such as moveable intransverse direction (“T”) or a lateral direction (“L”). Other degreesof freedom are possible, such as rotation about one or more other axes,such as rotation about a transverse axis (indicated as “R”).

The coordinate system (including axes A, T, and L) shown in FIG. 1A mayhave an origin located at an isocenter 110. The isocenter may be definedas a location where the radiation therapy beam 108 intersects the originof a coordinate axis, such as to deliver a prescribed radiation dose toa location on or within a patient. For example, the isocenter 110 may bedefined as a location where the radiation therapy beam 108 intersectsthe patient for various rotational positions of the radiation therapyoutput 104 as positioned by the gantry 106 around the axis A.

In an example, a detector 114 may be located within a field of thetherapy beam 108, such as may include a flat panel detector (e.g., adirect detector or a scintillation-based detector). The detector 114 maybe mounted on the gantry 106 opposite the radiation therapy output 104,such as to maintain alignment with the therapy beam 108 as the gantry106 rotates. In this manner, the detector 114 may be used to monitor thetherapy beam 108 or the detector may be used 114 for imaging, such asportal imaging of a projection of the beam 108 through the region 112.The region 112 may define a plane and a projection of the therapy beam108 in the region 112 may be referred to as a “Beam Eye View” of theregion 112.

In an illustrative example, one or more of the platform 116, the therapyoutput 104, or the gantry 106 may be automatically positioned, and thetherapy output 104 may establish the therapy beam 108 according to aspecified dose for a particular therapy delivery instance. A sequence oftherapy deliveries may be specified according to a radiation therapytreatment plan, such as using one or more different orientations orlocations of the gantry 106, platform 116, or therapy output 104. Thetherapy deliveries may occur sequentially, but may intersect in adesired target region on or within the patient, such as at the isocenter110. A prescribed cumulative dose of radiation therapy may thereby bedelivered to the target region while damage to tissue nearby the targetregion, such as one or more organs-at-risk, is reduced or avoided.

As mentioned in relation to other examples herein, the radiation therapysystem 102 may include or may be coupled to an imaging acquisitionsystem, such as to provide one or more of nuclear magnetic resonance(MR) imaging, or X-ray imaging, such as may include computed tomography(CT) imaging. In an example, MR imaging information or other imaginginformation may be used to generate imaging information orvisualizations equivalent to CT imaging, without requiring actual CTimaging. Such imaging may be referred to as “pseudo-CT” imaging.

FIG. 1B illustrates generally a partially cut-away view of an example ofa system that including a combined radiation therapy system 102 and anuclear magnetic resonance (MR) imaging system 130. The MR imagingsystem 130 may be arranged to define a “bore” around an axis (“A”), andthe radiation therapy system may include a radiation therapy output 104,such as to provide a radiation therapy beam 108 directed to an isocenter110 within the bore along the axis, A. The radiation therapy output 104may include a collimator 124, such as to one or more of control or shapethe radiation therapy beam 108 to direct the beam 108 to a target regionwithin a patient. The patient may be supported by a platform, such as aplatform positionable along one or more of an axial direction, A, alateral direction, L, or a transverse direction, T. One or more portionsof the radiation therapy system 102 may be mounted on a gantry 106, suchas to rotate the radiation therapy output 104 about the axis A.

FIG. 1A and FIG. 1B illustrate generally examples including aconfiguration where a therapy output may be rotated around a centralaxis (e.g., an axis “A”). Other radiation therapy output configurationsmay be used. For example, a radiation therapy output may be mounted arobotic arm or manipulator, such as having multiple degrees of freedom.In yet another example, the therapy output may be fixed, such as locatedin a region laterally separated from the patient, and a platformsupporting the patient may be used to align a radiation therapyisocenter with a specified target region within the patient.

FIG. 2 illustrates generally an example of a multi-leaf collimator (MLC)configuration 132, such as may be used in part to shape or collimate aradiation therapy beam. In FIG. 2, leaves 132A through 132J may beautomatically positioned to define an aperture approximating a tumor 140cross section or projection. The leaves 132A through 132J may be made ofa material specified to attenuate or block the radiation beam in regionsother than the aperture, in accordance with the radiation treatmentplan. For example, the leaves 132A through 132J may include metallicplates, such as comprising tungsten, with a long axis of the platesoriented parallel to a beam direction, and having ends orientedorthogonally to the beam direction (as shown in the plane of theillustration of FIG. 2).

A “state” of the MLC 132 may be adjusted adaptively during a course ofradiation therapy, such as to establish a therapy beam that betterapproximates a shape or location of the tumor 140 or other targetedregion, as compared to using a static collimator configuration or ascompared to using an MLC 132 configuration determined exclusively usingan “offline” therapy planning technique. A radiation therapy techniqueincluding using the MLC 132 to produce a specified radiation dosedistribution to a tumor or to specific areas within a tumor may bereferred to as Intensity Modulated Radiation Therapy (IMRT). Asdescribed in relation to other examples herein, imaging may be performedto localize the target region or to determine or predict a perspectiveof a target region from the point-of-view of the radiation therapy beamto adaptively guide therapy.

FIG. 3 illustrates generally an example of radiation therapy system 300,such as may include a radiation therapy device 330 and an imagingacquisition device. Radiation therapy system 300 may include a trainingmodule 312, a prediction module 314, a training database 322, a testingdatabase 324, a radiation therapy device 330, and an image acquisitiondevice 350. Radiation therapy system 300 may also be connected to atreatment planning system (TPS) 342 and an oncology information system(OIS) 344, which may provide patient information. In addition, radiationtherapy system 300 may include a display device and a user interface.

FIG. 4 illustrates generally an example of a system 400 that may be usedfor one or more of imaging acquisition, image segmentation, targetprediction, therapy control, or therapy adjustment. According to someembodiments, system 400 may be one or more high-performance computingdevices capable of identifying, analyzing, maintaining, generating, orproviding large amounts of data consistent with the disclosedembodiments. System 400 may be standalone, or it may be part of asubsystem, which in turn may be part of a larger system. For example,system 400 may represent distributed high-performance servers that areremotely located and communicate over a network, such as the Internet,or a dedicated network, such as a local area network (LAN) or awide-area network (WAN). In some embodiments, system 400 may include anembedded system, imaging scanner (e.g., a nuclear magnetic resonance(MR) scanner or other scanner such as a computed tomography (CT)scanner), and/or touch-screen display device in communication with oneor more remotely located high-performance computing devices.

In one embodiment, system 400 may include one or more processors 414,one or more memories 410, and one or more communication interfaces 415.Processor 414 may be a processor circuit, including one or moregeneral-purpose processing devices such as a microprocessor, centralprocessing unit (CPU), graphics processing unit (GPU), or the like. Moreparticularly, processor 414 may be a complex instruction set computing(CISC) microprocessor, reduced instruction set computing (RISC)microprocessor, very long instruction Word (VLIW) microprocessor, aprocessor implementing other instruction sets, or processorsimplementing a combination of instruction sets.

Processor 414 may also be one or more special-purpose processing devicessuch as an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA), a digital signal processor (DSP), aSystem-on-a-Chip (SoC), or the like. As would be appreciated by thoseskilled in the art, in some embodiments, processor 414 may be aspecial-purpose processor, rather than a general-purpose processor.Processor 414 may include one or more known processing devices, such asa microprocessor from the Pentium™ or Xeon™ family manufactured byIntel™, the Turion™ family manufactured by AMD™, or any of variousprocessors manufactured by other vendors such as Oracle™ (e.g., aSPARC™—architecture processor). Processor 414 may also include graphicalprocessing units manufactured by Nvidia™. The disclosed embodiments arenot limited to any type of processor(s) otherwise configured to meet thecomputing demands of identifying, analyzing, maintaining, generating,and/or providing large amounts of imaging data or any other type of dataconsistent with the disclosed embodiments.

Memory 410 may include one or more storage devices configured to storecomputer-executable instructions used by processor 414 to performfunctions related to the disclosed embodiments. For example, memory 410may store computer executable software instructions for treatmentplanning software 411, operating system software 412, andtraining/prediction software 413. Processor 414 may be communicativelycoupled to the memory/storage device 410, and the processor 414 may beconfigured to execute the computer executable instructions storedthereon to perform one or more operations consistent with the disclosedembodiments. For example, processor 414 may execute training/predictionsoftware 413 to implement functionalities of training module 312 andprediction module 314. In addition, processor device 414 may executetreatment planning software 411 (e.g., such as Monaco® provided byElekta) that may interface with training/prediction software 413.

The disclosed embodiments are not limited to separate programs orcomputers configured to perform dedicated tasks. For example, memory 410may include a single program that performs the functions of the system400 or multiple programs (e.g., treatment planning software 411 and/ortraining/prediction software 413). Additionally, processor 414 mayexecute one or more programs located remotely from system 400, such asprograms stored in database 420, such remote programs may includeoncology information system software or treatment planning software.Memory 410 may also store image data or any other type ofdata/information in any format that the system may use to performoperations consistent with the disclosed embodiments.

Communication interface 415 may be one or more devices configured toallow data to be received and/or transmitted by system 400.Communication interface 415 may include one or more digital and/oranalog communication devices that allow system 400 to communicate withother machines and devices, such as remotely located components ofsystem 400, database 420, or hospital database 430. For example,Processor 414 may be communicatively connected to database(s) 420 orhospital database(s) 430 through communication interface 415. Forexample, Communication interface 415 may be a computer network, such asthe Internet, or a dedicated network, such as a LAN or a WAN.Alternatively, the communication interface 415 may be a satellitecommunications link or any form of digital or analog communications linkthat allows processor 414 to send/receive data to/from eitherdatabase(s) 420, 430.

Database(s) 420 and hospital database(s) 430 may include one or morememory devices that store information and are accessed and managedthrough system 400. By way of example, database(s) 420, hospitaldatabase(s) 530, or both may include relational databases such asOracle™ databases, Sybase™ databases, or others and may includenon-relational databases, such as Hadoop sequence files, HBase,Cassandra or others. The databases or other files may include, forexample, one or more of raw data from MR scans or CT scans associatedwith an imaging subject, such as for training or providing a referenceimage, MR feature vectors, MR projection imaging information, CT values,reduced-dimension feature vectors, pseudo-CT prediction model(s),pseudo-CT value(s), pseudo-CT image, DICOM data, etc. Systems andmethods of disclosed embodiments, however, are not limited to separatedatabases. In one aspect, system 400 may include database(s) 420 orhospital database(s) 430. Alternatively, database(s) 420 and/or hospitaldatabase(s) 430 may be located remotely from the system 400. Database(s)420 and hospital database(s) 430 may include computing components (e.g.,database management system, database server, etc.) configured to receiveand process requests for data stored in memory devices of database(s)420 or hospital database(s) 430 and to provide data from database(s) 420or hospital database(s) 430.

System 400 may communicate with other devices and components of system400 over a network (not shown). The network may be any type of network(including infrastructure) that provides communications, exchangesinformation, or facilitates the exchange of information and enables thesending and receiving of information between other devices and/orcomponents of system 400 over a network (not shown). In otherembodiments, one or more components of system 400 may communicatedirectly through a dedicated communication link(s), such as a link(e.g., hardwired link, wireless link, or satellite link, or othercommunication link) between system 400 and database(s) 420 and hospitaldatabase(s) 430.

The configuration and boundaries of the functional building blocks ofsystem 400 has been defined herein for the convenience of thedescription. Alternative boundaries may be defined so long as thespecified functions and relationships thereof are appropriatelyperformed. Alternatives (including equivalents, extensions, variations,deviations, etc., of those described herein) will be apparent to personsskilled in the relevant art(s) based on the teachings contained herein.

FIG. 5 illustrates generally an example of a system 500, such as mayinclude a radiation therapy controller system 554 having an imaginginput 560, a radiation therapy generator 556, and a radiation therapyoutput 504. The therapy generator 556 may include an accelerator, suchas a linear accelerator, or another source of radiation, and the therapyoutput 504 may be coupled to the therapy generator 556 to process a beamof energetic photons or particles provided by the therapy generator 556.For example, the therapy output 504 may include or may be coupled to anoutput actuator 566 to one or more of rotate or translate the therapyoutput 504 to provide a radiation therapy beam directed to a desiredtarget region. The therapy output 504 may include a collimator 564, suchas a multi-leaf collimator as mentioned above in relation to FIG. 2.Referring back to FIG. 5, the therapy controller system 554 may beconfigured to control one or more of the therapy generator 556, thetherapy output 504, or a patient position actuator 516 (such as amovable platform including a couch or table), using an adaptiveradiation treatment technique as described in other examples herein.

The therapy controller system 554 may be coupled to one or more sensors,such as using a sensor input 562. For example, a patient sensor 558 mayprovide physiologic information to the therapy controller system, suchas information indicative of one or more of respiration (e.g., using aplethysmographic sensor or respiration belt), patient cardiac mechanicalor electrical activity, peripheral circulatory activity, patientposition, or patient motion. Such information may provide a “surrogate”correlated with motion of one or more organs or other regions to betargeted by the therapy output 504. Such information may be used tocontrol therapy such as for therapy gating or to assist in “binning”acquired imaging information according to one or more of a determinedphase or amplitude range of a physiologic cycle as indicated by obtainedinformation from the sensor 558.

The imaging input 560 may be coupled to an imaging system 550 (such asmay include a computed tomography imaging system or a nuclear magneticresonance (MR) imaging system, as illustrative examples). Alternatively,or in addition, the therapy controller system 554 may receive imaginginformation from an imaging data store 552, such as a centralizedimaging database or imaging server. One or more of the therapycontroller system 554 or the imaging system 550 may include elementsshown and described in relation to the system 400 shown in FIG. 4.

Generally-available radiation therapy equipment can be used to acquireprojection images using X-ray imaging techniques. For example, linearaccelerator (linac) systems can acquire X-ray projection images usingone or more of the megavoltage (MV) treatment beam itself combined witha portal imaging device (such as shown illustratively in FIG. 1A) orusing one or more separate kilovolt (kV) X-ray sources. In an example, akV X-ray source can be mounted on a gantry such as oriented at a90-degree angle with respect to the treatment beam orientation. Inanother example, two independent X-ray source/imager pairs can belocated to provide stereoscopic X-ray imaging. Projection imagesacquired using X-ray imaging represent a divergent X-ray path from theimaging source, which can be referred to as a “point source” or focalpoint.

Prior to delivery of radiation therapy, such as prior to a particularradiation therapy treatment fraction, X-ray computed tomography (CT)images may be acquired. For example, a cone-beam CT (CBCT) imagingtechnique can be used to obtain projection images at various projectionangles during a rotation of a gantry-mounted X-ray source around animaging subject. A three-dimensional (3D) image can be reconstructedfrom such cone beam projections. For imaging subjects that exhibitsignificant motion, such as respiratory motion, 3D CBCT images may beblurred because each projection may capture a snapshot of the patient ata different point in the respiration cycle or other physiologic cycle.To reduce motion blurring, four-dimensional (4D) CBCT imaging may beused, such as by binning projections according to a phase or amplitudeof the physiologic cycle corresponding to the time at which theprojection image was acquired.

The present inventors have recognized, among other things, that nuclearmagnetic resonance (MR) imaging projections can be similarly acquiredand processed, such as reducing exposure of the imaging subject toionizing radiation and providing enhanced soft tissue contrast ascompared to X-ray-based imaging approaches. The present inventors havealso recognized, among other things, that MR projection images are notdegraded by scattered radiation, and the projection imaging direction isnot limited by physical constraints such as having to be oriented at 90degrees relative to the treatment beam. MR projection imaging can beused to acquire a single imaging perspective (e.g., a 2D projectionimage) of all of the information contained within a depth extent of anexcited imaging region, as opposed to using relatively thin 2D MRimaging slices which capture only a portion of the information in adepth direction. MR projection imaging does have limitations, such asthat information in an acquired 2D projection image is not localized inthe depth direction orthogonal to the projection imaging plane, andstructures surrounding a targeted region can appear to partially maskit.

MR Projection Imaging Such as Using 1D Projection Lines

FIG. 6 illustrates generally a technique 600, such as a method, that mayinclude at 602 using MR imaging to excite a region of an imagingsubject. For example, a two-dimensional (2D) excitation sequence may beused. At 604, a readout gradient may be applied to the imaging subject,and a one-dimensional (1D) projection line (e.g., a “ray”) through the2D excited region may be acquired. At 606, another projection line axismay be selected, and a 2D region is again excited at 602, and a readoutgradient is applied at 604 corresponding to the updated projection lineaxis. Referring to the inset diagrams at 606, the projection lines maybe established in a divergent manner or a parallel manner. For example,if divergent projection line orientations are used, a resultingprojection image defined in the plane 670A may provide a projectionrepresentation that is similar to projection images produced bydivergent X-ray imaging techniques, or similar to a projection imageproduced by a radiation therapy output beam during portal imaging. Inthis manner, MR projection imaging can be used to simulate X-rayimaging, but with enhanced contrast and without undesired scattering,for example.

In the example of divergent MR projection imaging using 1D projectionlines, the 1D projection lines can be specified to converge at alocation 650, such as corresponding to a location of a radiation therapybeam source or corresponding to a location where an X-ray imaging sourcewould generally reside. A scale and spatial resolution of informationdefined in a resulting 2D projection image established in the plane 670Amay be determined by the distance between the source location 650 and aselected imaging plane 670A location. For example, a first projectionline orientation 660A can be orthogonal to the projection imaging plane670A, and a corresponding acquired 1D projection line can be used toestablish a pixel value at a location 680A. All information acquiredalong the first projection line is generally incorporated and compressedinto the pixel value, thus depth selectivity is lost in the directionalong the projection line.

The line orientation 660A orthogonal to the projection imaging plane670A may generally be referred to as the projection “direction” or“angle” even though in divergent examples, other projection lineorientations are not parallel. A second projection line orientation 662Acan similarly establish a second pixel value at a location 682A, and athird projection line orientation 664A can similarly establish a thirdpixel value at a location 684A. In a reconstructed image, the pixellocations 680A, 682B, and 684B are determined at least in part by aspecified separation between the plane 670A location and the sourcelocation 650. To achieve higher spatial resolution in a lateraldirection in plane 670A, a greater number of separate 1D projection linedirections can be acquired at the cost of total 2D projection imageacquisition duration, because particular acquired 1D projections areaggregated to create a full 2D projection in the plane 670A.

In a parallel 1D projection line example, such as at 606, a firstprojection line orientation 660B can be established to provide a firstpixel value at a location 680B in a resulting projection image definedin the plane 670B. Other parallel lines 662B and 664B can be used toprovide information for corresponding location 682B and 684B in theprojection image. As a practical consideration, if exclusively parallel1D projection lines are being used to construct a particular 2Dprojection image, the techniques of FIG. 7A or FIG. 7B may provideenhanced efficiency as compared to the example of FIG. 6 because a 2Dprojection image can be reconstructed directly by suppressing a sliceselection gradient or by using a large slice thickness (relative to adepth extent of interest) without requiring excitation and readout ofparticular 1D projection lines.

Parallel projection can provide one or more of a simplified geometrycompared to a divergent approach, one-to-one correspondence betweenprojection image pixels and a plane defining a “beam eye view,” oreasier tomographic reconstruction from multiple projections. Bycomparison, X-ray-based CBCT tomographic reconstruction is generallyonly approximate due to divergence of the acquired cone-beam projectionimages. In either the divergent or parallel 1D projection line examples,the spacing or orientation of the projection lines need not be uniformand may be specified depending on a variety of factors. For example, aspatial resolution in a direction of predicted motion of a target withinthe field of view of the projection image and parallel to the projectionimage plane may be enhanced by increasing a spatial frequency ofprojection lines in the direction of predicted motion. Similarly,shorter total acquisitions can be provided by using a more sparse set ofdivergent projection lines.

MR Projection Imaging Such as Using 2D Excitation without RequiringSlice Selection Gradient or Using Large Slice Depth Encompassing a Depthof Interest

FIG. 7A illustrates generally a technique 700A, such as a method, thatmay include exciting a region of an imaging subject using atwo-dimensional (2D) MR imaging excitation sequence at 702. FIG. 7Billustrates generally another technique 700B, such as a method, that mayalso include exciting a region of an imaging subject using atwo-dimensional (2D) MR imaging excitation sequence at 702.

In the example of FIG. 7A, a 2D MR projection image can be obtained at704A by using a 2D imaging sequence without requiring use of a sliceselection gradient (e.g., the slice selection gradient pulse sequencecan be suppressed or omitted) so that information in a depth direction(e.g., in the projection imaging direction and perpendicular to a planeof a resulting projection image) is acquired at all depths within theexcited region. Such an approach does not require excitation andgradient readout of 1D projection lines and can therefore reduce imageacquisition duration as compared to a 1D projection approach in the casewhere parallel 1D projection lines are desired.

In the example of FIG. 7B, a 2D MR projection image can be obtained at704B by using a 2D imaging sequence using a slice selection gradientdefining a slice sufficiently large in depth to encompass a region ofdepth of interest, such as corresponding to a portion or an entirety ofa radiation therapy target extent in a dimension parallel to theprojection angle. As the slice thickness is increased, the depthdimension of the slice includes more and more anatomical contribution ofinformation that was previously out-of-field in depth. Such depthinformation is compressed into a single point or pixel location in theresulting 2D projection image. The technique 700B of FIG. 7B similarlyoffers a reduced image acquisition duration as compared to the 1Dprojection approach and can be referred to as a “very thick slice”projection approach.

MR imaging data can also be obtained in “k-space,” representing acoordinate space corresponding to the spatial Fourier transform of theimaging information. For example, MR imaging data can be naturallycollected in k-space by varying image gradients; a particularcombination of x, y and z gradients generally corresponds to a singlepoint in k-space. By sequentially filling the points in k-space, aninverse Fourier Transform can then be applied to the k-spacerepresentation to generate an image. A 2D plane in k-space correspondsto a 2D projection in image space. Accordingly, a 2D projection can alsobe obtained by acquiring k-space points that lie in a plane in k-space,and generating a 2D inverse Fourier Transform on the plane in k-space (ak-space slice) to obtain a 2D projection in image space.

Three-Dimensional (3D) and Four-Dimensional (4D) Imaging Using MRProjection Imaging Such as Correlated with a Physiologic Cycle

FIG. 8A illustrates generally a technique 800A, such as a method, thatmay include generating two-dimensional (2D) MR projection images such asrepresentative of different projection angles, and using such 2Dprojection images to construct three-dimensional (3D) images. Acorresponding technique 800B is shown schematically in FIG. 8B.

At 802A a series of 2D MR projection images can be generated, such asusing one or more techniques mentioned elsewhere herein as shown, forexample, in FIG. 6 (by aggregating 1D projection lines), or as shown inFIG. 7A or FIG. 7B. Referring to FIG. 8B at 802B, 2D projection imagesP₁, P₂, P₃, . . . , PN can be acquired at different projection angles.For example, projection angles can be specified to capture projectiondirections around the imaging subject. Tomographic reconstruction maythen be performed to obtain a 3D image. As the projection directionrotates around the patient, tomographic reconstruction techniques, suchas similar to X-ray techniques including CT or CBCT reconstruction, canused to either create a new 3D image, or update a previous 3D image withnew information.

However, motion may induce blurring in reconstructed 3D images.Accordingly, in FIG. 8A at 804A, particular acquired 2D projectionimages can be assigned to bins using information indicative of atemporal position within a physiologic cycle, such as respiration. Suchbinning can be accomplished using information obtained from one or moreof a surrogate, an external marker, or an internal marker or feature.For example, to obtain information indicative of a respiration cycle, arespiration belt can be used to provide a surrogate signal or diaphragmmotion can be tracked in acquired imaging information.

Referring to FIG. 8B, at 804B, f(t) can represent a plot of a signalrepresentative of a portion of a physiologic cycle such as respiration.Various bins such as phase bins ϕ₁, ϕ₂, ϕ₃, . . . , ϕ_(n) can beestablished, such as corresponding to portions (e.g., a range Δt) alongf(t). Acquired 2D projection images can be assigned to bins ϕ₁, ϕ₂, ϕ₃,. . . , ϕ_(n) such as by determining a portion of f(t) on which aparticular acquired image falls. The use of phase-based bins is merelyillustrative and amplitude bins could similarly be used, such ascorresponding to amplitude ranges (e.g., a range Δf) along f(t).

Referring to FIG. 8A, at 806A a 3D image can be constructed using abinned series of 2D projection images corresponding to differentprojection angles. In the context of FIG. 8B, at 806B, the 3D images I₁,I₂, I₃, . . . , I_(n) can correspond to each of the bins ϕ₁, ϕ₂, ϕ₃, . .. , ϕ_(n). Referring to FIG. 8A, at 808A, 4D imaging information can beconstructed by aggregating the 3D images constructed at 806A. In thecontext of FIG. 8B, the series of 3D images can provide a 4Drepresentation of imaged region of the subject throughout thephysiologic cycle. Motion induced by a physiologic cycle such asrespiration may generally be highly periodic and reproducible.

MR Projection Imaging for Radiation Therapy Control

FIG. 9 illustrates generally a technique, such as a method, that mayinclude generating a two-dimensional (2D) projection image using MRimaging and determining a change between the generated 2D projectionimage and reference imaging information. At 902, reference imaginginformation can be received. For example, the techniques 800A or 800B ofFIG. 8A or FIG. 8B can be used to obtain reference imaging information,such as prior to treatment. In another example, a particular 3Dreference image can also be generated, without requiring generation ofother 3D images or aggregation of the acquired 3D images into 4D imaginginformation. For example, if respiration-gated therapy is to bedelivered during a particular phase or amplitude of a respiration cycle,one or more 3D images can be constructed corresponding to a portion ofthe respiration cycle of interest, either during pre-treatment planningor intrafractionally.

At 904, a 2D projection image can be generated using techniques shownand described elsewhere herein (e.g., using a 2D MR imaging sequencewith a large slice selection gradient or no slice selection gradient, orby aggregating information acquired corresponding to multiple 1Dprojection lines). At 906, a change between a generated 2D projectionimage and reference imaging information can be determined. At 908,delivery of the radiation therapy may be controlled at least in partusing information indicative of the determined change.

The determined change can provide information indicative of one or moreof an updated location of a target region, an anatomical feature orlandmark, or a motion of the target region, anatomical feature, orlandmark, as illustrative examples. In an example, the 2D MR projectionimage generated at 904 can include or can be related to target motionfrom the perspective of a radiation therapy “beam eye view” (BEV) plane.There are various ways that the target motion in the BEV plane can beextracted from a 2D MR projection image.

In one approach, a 2D/3D registration can be performed between the 2D MRprojection image and 3D MR imaging information, such as in a mannersimilar to techniques used for registration between an X-ray projectionimage and a reference CT or CBCT image. Such an approach can be used,for example, to identify one or more translations that provide a matchbetween the 2D projection image and shifted 3D MR imaging information,and the identified translation can be used as a the “change” in thecontext of FIG. 9 at 906 and 908 to control delivery, such as byrepositioning one or more of the therapy beam output or the patient, orby modifying the therapy beam aperture. A quality of the match can bedefined such as using one or more metrics, such as may includedetermining normalized cross-correlation or mutual information.Rotations and deformations may be included in the registration techniqueat the cost of simplicity and computational efficiency.

In another approach, a dimensionality reduction can be performed, suchas to transform a 2D/3D registration problem into a 2D/2D registrationproblem. In one approach, reference projections can be extracted from 3Dreference MR imaging information, in a manner similar to digitallyreconstructed radiographs (DRRs) in X-ray based radiotherapy imaging.Segmentation can be used, such as to identify a target or surroundingstructures such as OARs, though one more of the radiation therapy targetor OARs may be masked by structures that lie in the path of theprojection direction. Once the target or other structure has beensegmented, a motion of the target or other structure can be identified.Such motion an also be used to predict a future location of the target.

A challenge can exist in attempting to register or otherwise comparelater-acquired MR projection images with reference 3D or 4D MR imaginginformation. Later-acquired MR projection images may have differentimage quality than the reference imaging information, particularly whenthe reference imaging information was acquired without use of projectionimaging. Registration techniques are generally more effective incomparing images having similar image quality or characteristics. Thepresent inventors have recognized, among other things, that thereference imaging information (such as received at 902 in FIG. 9) can beacquired using MR projection imaging, such as using a rotating set ofprojections.

As mentioned in relation to FIG. 8A and FIG. 8B, such MR projections canbe used to reconstruct a 3D MR image, such as using a tomographicreconstruction technique. In this manner, the reference 3D MR image willhave similar image quality as later-acquired MR projection images. In anexample, a later-acquired MR projection image can be compared directlyto an acquired reference MR projection image without requiring use of 3Dor 4D reference imaging information.

As mentioned above, if projection directions are rotated around theimaging subject, 4D MR reference imaging information can be compiled inmanner similar to 4D-CBCT, because particular projections will generallycontain different views of the anatomy of the imaging subject. Suchanatomy may include landmarks such as showing a diaphragm location, or aregion to be targeted by radiation. Common anatomical landmarks can thenbe used to bin the projections to form the 4D MRI sequence, rather thanusing an independent surrogate.

An acquisition duration to obtain 3D or 4D imaging information can becontrolled using MR projection imaging techniques. For example, anacquisition duration can be shortened significantly such as by acquiringa more limited number of tomographic projections and using sparsetomographic reconstruction techniques such as compressed sensing orprior image compressed sensing (PICCS). An acquisition duration can alsobe improved such as by using parallel imaging strategies including oneor more of multiple transmit or receive coils with different sensitivityprofiles.

In the examples described herein, MR projections need not includeprojection profiles that encompass an entirety of the patient in thedepth dimension along the projection direction. For example, aparticular MR projection image may use a finite slice thicknessencompassing an entirety of the region of interest in the depthdimension. Reducing an extent of the depth dimension can help to reduceobscuration of the region of interest (e.g., shadowing) by overlying orunderlying anatomy in the depth dimension, but at the expense ofreducing or eliminating an ability to provide full tomographicreconstruction.

MR Projection Imaging Spatial Arrangements Such as Relative to RadiationTherapy Beam Orientation

FIG. 10A illustrates generally a spatial arrangement of a radiationtherapy beam orientation 1090 with respect to one or more projectiondirections, such as may include two projection directions orientedorthogonally to each other. In the simplest approach, an MR projectionimage can be acquired using a projection line orientation 1060A thatcoincides with the therapy beam orientation 1090, at first angularposition θ_(A). As mentioned in relation to other examples, a projectionimaging plane 1070A can include information acquired using parallelprojection (e.g., such as corresponding to lines 1064A and 1062A), orusing a divergent projection line orientation, converging at a location1050. The MR projection image can obtain information along theprojection lines to encompass a region of interest 1012, such asincluding a treatment isocenter 1010. In this manner, the projectionimaging plane 1070A can provide an imaging representation similar to abeam eye view (BEV) or portal image.

The configuration shown in FIG. 10A can be static, or the beamorientation and projection line orientation can be rotating togetheraround the patient (as in the example of a gantry-mounted treatment beamoutput providing portal imaging). An orientation for MR projectionimaging aligned with the BEV is generally a useful direction because theaperture of the therapy beam is generally shaped to provide a specifiedprofile in the plane parallel to the projection imaging plane 1070A.Without imaging from other directions, motion of a target or imagingfeatures may not be explicitly determined in the depth direction (e.g.,Y direction), but approaches exist to estimate such motion if in-planeinformation indicative of target motion is available. Otherwise,additional projections can be acquired having other projectiondirections.

In an example, one or more MR projections perpendicular to a BEV planemay be acquired, such as at various different times. Such orthogonalimages can help to obtain information missing in the depth direction(e.g., Y direction) along the first projection line orientation 1060A.For example, as shown illustratively in FIG. 10A, a second projectionline orientation 1060B can be used at an orthogonal angular positionθ_(B), defining a projection imaging plane 1070B orthogonal to the firstprojection imaging plane 1070A. Again, parallel or divergent projectionlines can be established, such as the parallel lines 1064B and 1062Bshown in FIG. 10A.

Alternating or otherwise sequencing between projections parallel andperpendicular to the BEV plane can provide full depth information, atthe expense of a reduced acquisition frequency of projections parallelto the BEV. The orthogonal configuration shown in FIG. 10A can simulategantry-mounted x-ray based stereoscopic imaging. As an illustrativeexample, the perpendicular projections need not be acquired alternatelyfor every BEV projection acquisition. For example, the orthogonalprojection orientation may be used for acquisition only occasionally toestablish or update a correlation between target motion in the BEV andmotion in the depth direction.

FIG. 10B illustrates generally a spatial arrangement of MR imagingprojection directions 1060A, 1060B, and 1060C, such as corresponding toprojection angle positions θ_(A), θ_(B), θ_(C) spanning an arc or circleabout a specified region such as a radiation therapy treatment isocenter1010. The respective projection directions 1060A, 1060B, and 1060C canprovide particular projection imaging plane orientations 1070A, 1070B,and 1070C. For rotational radiation therapy treatment deliveries, theBEV naturally rotates around the patient, such as when the radiationtherapy source is mounted on a gantry. Acquired projection images canhave more than one purpose. For example, as mentioned above, aparticular BEV projection image can provide information indicative of aradiation therapy target position or shape from the perspective of theradiation therapy beam source. Also, if a series of projection imagesare acquired, a 3D tomographic MR image can be reconstructed. The MRprojection orientations shown in FIG. 10B are not limited to exampleswhere the radiation therapy beam source is rotated. For example, forradiation therapy involving one or more static therapy fields, rotatingMR projections can be acquired separately from the BEV projections, suchas in an alternating fashion or according to another specified imagingsequence.

FIG. 10C illustrates generally a spatial arrangement of an MR imagingprojection direction 1060D, such as oriented at a specified angle, a,with respect to a radiation therapy beam direction. The radiationtherapy beam 1090 can diverge from a source location 1050, and a plane1092 can define the BEV. By contrast with other examples, the MR imagingprojection direction 1060D can be specified to capture an imagingperspective slightly different from the BEV projection, such as toobtain imaging information corresponding to a temporally-advanced BEVoffset from a current BEV. Such temporally-advanced MR projectionimaging can include an angle α specified to account for time lagassociated with one or more of MR projection imaging acquisition,correction of the radiation therapy delivery protocol, or updating ofthe radiation therapy delivery protocol in response to acquired MRprojection imaging. As in other examples, parallel or divergent MRprojection imaging schemes can be used, and also as in other examples,the projection line orientation 1060D can be rotated relative to theradiation therapy beam orientation as the radiation therapy beam isrotated around the patient.

The advance angle α can be determined using information about one ormore of a known lag duration or the angular speed of a beam-positioninggantry, as an illustrative example. A prediction technique can beapplied to information acquired from the “advance BEV plane” 1070D suchas to predict the most likely target position that will occur by thetime the therapy output beam position catches up with the alignment ofthe advance BEV plane 1070D. Examples of prediction techniques caninclude one or more of kernel density estimation, wavelet-basedtechniques, or relevance vector machine (RVM) techniques. Adimensionality of the prediction problem can be reduced from threedimensions to two dimensions, because projected motion may be confinedto the advance BEV plane 1070D perspective rather than having to predicttarget motion in a three-dimensional coordinate space.

FIG. 10D illustrates generally a spatial arrangement of MR imagingprojection directions 1060E and 1060F, such as may be specified toprovide MR projection images in projection planes 1070E and 1070F in amanner similar to stereoscopic X-ray imaging. In the example of FIG.10D, a projection image need not be acquired in the BEV direction, butmay still be acquired using fixed orientations such as simulatingroom-mounted stereoscopic X-ray imaging techniques. As an illustrativeexample, alternating MR projections in the anterioposterior and lateraldirections can be acquired such as to help locate a radiation therapytarget or other anatomical features. In an example, a combination MRprojection directions such as fixed orientations and rotatingorientations corresponding to gantry position can be used. As anillustrative example, three or more projections can be acquired, such asin an alternating fashion, including a projection oriented to coincidewith the BEV; an anterioposterior projection; and a lateral projection.Each of the projections can be selected to include a path traversing aspecified region of the imaging subject, such as the treatment isocenter1010. Such projections do not need each need to be acquired at the sameimaging rate.

Various Notes & Examples

Example 1 can include or use subject matter (such as an apparatus, amethod, a means for performing acts, or a device readable mediumincluding instructions that, when performed by the device, can cause thedevice to perform acts), such as can include a method for generatingfour-dimensional (4D) imaging information representative of aphysiologic cycle of a subject, the method comprising: generating two ormore two-dimensional (2D) images, the 2D images comprising projectionimages representative of different projection angles, and the 2D imagesgenerated using imaging information obtained via nuclear magneticresonance (MR) imaging; assigning the particular 2D images to bins atleast in part using information indicative of temporal positions withinthe physiologic cycle corresponding to the particular 2D images;constructing three-dimensional (3D) images using the binned 2D images;and constructing the 4D imaging information, comprising aggregating the3D images.

In Example 2, the subject matter of Example 1 optionally includes: aphysiologic cycle comprising a respiration cycle; and obtaining the twoor more 2D images comprising obtaining 2D images representative ofdifferent projection angles over a duration spanning multiplerespiration cycles.

In Example 3, the subject matter of any one or more of Examples 1-2optionally includes generating two or more 2D projection imagesincluding aggregating acquired one-dimensional (1D) projection linesinto a particular 2D image, the 1D projection lines oriented spatiallyparallel to one another.

In Example 4, the subject matter of any one or more of Examples 1-3optionally includes generating two or more 2D projection imagesincluding aggregating acquired one-dimensional (1D) projection linesinto a particular 2D image, the 1D projection lines oriented tospatially diverge from one another.

In Example 5, the subject matter of any one or more of Examples 1-4optionally includes generating two or more 2D projection imagesincluding acquiring a 2D MR imaging slice perpendicular to a projectionangle without requiring a slice selection gradient.

In Example 6, the subject matter of any one or more of Examples 1-5optionally includes generating two or more 2D projection imagesincluding acquiring a 2D MR imaging slice perpendicular to a projectionangle using a slice selection gradient defining a slice sufficientlylarge in depth to encompass an entirety of a radiation therapy targetextent in a dimension parallel to the projection angle.

In Example 7, the subject matter of any one or more of Examples 1-6optionally includes projection angles spanning an arc rotating about aspecified central axis.

In Example 8, the subject matter of any one or more of Examples 1-7optionally includes determining a phase of a portion of the physiologiccycle corresponding to particular 2D images; and assigning theparticular 2D images to bins using information indicative of thedetermined phase.

In Example 9, the subject matter of any one or more of Examples 1-8optionally includes determining an amplitude of a portion of thephysiologic cycle corresponding to particular 2D images; and assigningthe particular 2D images to bins using information indicative of thedetermined amplitude.

In Example 10, the subject matter of any one or more of Examples 1-9optionally includes one or more of the phase or amplitude of the portionof the physiologic cycle corresponding to particular 2D imagesdetermined using a feature extracted from the particular 2D images.

In Example 11, the subject matter of Example 10 optionally includes anextracted feature corresponding to a diaphragm of an imaging subject.

In Example 12, the subject matter of any one or more of Examples 1-11optionally includes, assigning the particular 2D images to bins using adimensionality reduction of acquired imaging information.

In Example 13, the subject matter of any one or more of Examples 1-12optionally includes assigning the particular 2D images to bins using aFourier Transform of the particular 2D images.

In Example 14, the subject matter of any one or more of Examples 1-13optionally includes constructing a 3D image from acquired 2D projectionimages using a tomographic image reconstruction technique.

In Example 15, the subject matter of any one or more of Examples 1-14optionally includes constructing the 3D image from the acquired 2Dprojection images including performing the 3D image construction usingtransformed imaging information represented in a Fourier space.

In Example 16, the subject matter of any one or more of Examples 1-15optionally includes constructing the 3D image from the acquired 2Dprojection images including performing the 3D image construction using afiltered back-projection technique.

In Example 17, the subject matter of any one or more of Examples 1-16optionally includes constructing the 3D image from the acquired 2Dprojection images including performing the 3D image construction using acompressed sensing technique.

In Example 18, the subject matter of any one or more of Examples 1-17optionally including constructing the 3D image from the acquired 2Dprojection images including performing the 3D image construction usingFeldman-Davis-Kress construction.

In Example 19, the subject matter of any one or more of Examples 1-18optionally includes constructing the 3D image from the acquired 2Dprojection images including performing the 3D image construction usingan iterative approach.

In Example 20, the subject matter of any one or more of Examples 1-19optionally includes providing the 4D imaging information for use ingenerating or adapting a radiation therapy treatment plan.

In Example 21, the subject matter of any one or more of Examples 1-20optionally includes using the 4D imaging information to assign ordetermine a position of the patient prior to delivery of a radiationtherapy treatment fraction.

Example 22 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 1-21 to include, subjectmatter (such as an apparatus, a method, a means for performing acts, ora machine readable medium including instructions that, when performed bythe machine, that can cause the machine to perform acts), such as caninclude a method to control radiation therapy delivery to a subjectusing projection imaging, the method comprising: receiving referenceimaging information; generating a two-dimensional (2D) projection imageusing imaging information obtained via nuclear magnetic resonance (MR)imaging, the 2D projection image corresponding to a specified projectiondirection, the specified projection direction including a pathtraversing at least a portion of an imaging subject; determining achange between the generated 2D projection image and the referenceimaging information; controlling delivery of the radiation therapy atleast in part using the determined change between the obtained 2Dprojection image and the reference imaging information.

In Example 23, the subject matter of Example 22 optionally includes,generating the 2D projection image comprising aggregating acquiredone-dimensional (1D) projection lines.

In Example 24, the subject matter of Example 23 optionally includes thatthe specified projection direction is specified at least in part toprovide 1D projection lines defined by respective paths traversing aradiation therapy treatment isocenter.

In Example 25, the subject matter of any one or more of Examples 23-24optionally includes that the 1D projection lines are oriented tospatially diverge from one another.

In Example 26, the subject matter of any one or more of Examples 23-25optionally includes that the directions corresponding to particular 1Dprojection lines are specified to converge in a location correspondingto an available position of a radiation therapy beam output.

In Example 27, the subject matter of any one or more of Examples 22-26optionally includes that generating the 2D projection image comprisesacquiring a 2D MR imaging slice perpendicular to a projection anglewithout requiring a slice selection gradient.

In Example 28, the subject matter of any one or more of Examples 22-27optionally includes that generating the 2D projection image comprisesacquiring a 2D MR imaging slice perpendicular to a projection angleusing a slice selection gradient defining a slice sufficiently large indepth to encompass an entirety of a radiation therapy target extent in adimension parallel to the projection angle.

In Example 29, the subject matter of any one or more of Examples 22-28optionally includes that the specified projection direction correspondsto a present or a future radiation therapy beam direction.

In Example 30, the subject matter of any one or more of Examples 22-29optionally includes that the specified projection direction isorthogonal to a present or a future radiation therapy beam direction.

In Example 31, the subject matter of any one or more of Examples 22-30optionally includes that the specified projection direction isestablished without requiring a radiation therapy beam direction.

In Example 32, the subject matter of any one or more of Examples 22-31optionally includes that the reference image comprises a second 2Dprojection image generated using earlier-acquired imaging information.

In Example 33, the subject matter of Example 32 optionally includes thatthe second 2D projection image is generated using four-dimensional (4D)imaging information assembled from earlier-acquired imaging information.

In Example 34, the subject matter of any one or more of Examples 22-33optionally includes that the reference image comprises three-dimensional(3D) imaging information corresponding to earlier-acquired imaginginformation.

In Example 35, the subject matter of any one or more of Examples 22-34optionally includes that the reference image comprises 4D imaginginformation assembled from earlier-acquired imaging information.

In Example 36, the subject matter of any one or more of Examples 22-35optionally includes that the reference image comprises a 3D imageextracted from a portion of 4D imaging information, the 4D imaginginformation assembled from earlier-acquired imaging information.

In Example 37, the subject matter of Example 36 optionally includes thatthe selected portion of the 4D imaging information comprises a specifiedportion of a physiologic cycle.

In Example 38, the subject matter of any one or more of Examples 22-37optionally includes that determining the change includes using a seriesof two or more 2D projection images generated using imaging informationobtained via nuclear magnetic resonance (MR) imaging.

In Example 39, the subject matter of any one or more of Examples 22-38optionally includes that determining the change includes registering atleast a portion of the 2D projection image with the reference image.

In Example 40, the subject matter of any one or more of Examples 22-39optionally includes that determining the change comprises extracting afeature from the 2D projection image.

In Example 41, the subject matter of any one or more of Examples 22-40optionally includes that determining the change includes segmenting aportion of the 2D projection image.

In Example 42, the subject matter of Example 41 optionally includes thatthe segmented portion of the 2D projection image comprises a perspectiveof a radiation therapy target.

In Example 43, the subject matter of any one or more of Examples 22-42optionally includes that determining the change comprises triangulatingbetween determined perspectives of the radiation therapy targetsegmented from two or more 2D projection images.

In Example 44, the subject matter of any one or more of Examples 22-43optionally includes predicting a location of a radiation therapy targetusing the determined change and a prediction model.

In Example 45, the subject matter of Example 44 optionally includes thatthe prediction model includes using information indicative of targetmotion established at least in part using extracted perspectives of theradiation therapy target from a series of acquired 2D projection imagesand the determined change between at least one 2D projection image andthe reference image.

Example 46 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 1-45 to include, subjectmatter (such as an apparatus, a method, a means for performing acts, ora machine readable medium including instructions that, when performed bythe machine, that can cause the machine to perform acts), such as caninclude an imaging system, comprising: at least one processor circuitand a processor-readable storage medium, the processor readable storagemedium including instructions that, when performed by the processorcircuit, cause the processor circuit to generate four-dimensional (4D)imaging information representative of a physiologic cycle of a subject,including: generating two or more two-dimensional (2D) images, the 2Dimages comprising projection images representative of differentprojection angles, and the 2D images generated using imaging informationobtained via nuclear magnetic resonance (MR) imaging; assigning theparticular 2D images to bins at least in part using informationindicative of temporal positions within the physiologic cyclecorresponding to the particular 2D images; constructingthree-dimensional (3D) images using the binned 2D images; andconstructing the 4D imaging information, comprising aggregating the 3Dimages.

Example 47 can include, or can optionally be combined with the subjectmatter of one or any combination of Examples 1-46 to include, subjectmatter (such as an apparatus, a method, a means for performing acts, ora machine readable medium including instructions that, when performed bythe machine, that can cause the machine to perform acts), such as caninclude a radiation therapy treatment system, comprising: a therapygenerator; and a therapy output; a therapy controller system coupled tothe radiation therapy generator and the radiation therapy output, theradiation therapy controller system comprising an imaging input, theimaging input configured to receive reference imaging information, thetherapy controller system configured to: generate a two-dimensional (2D)projection image using imaging information obtained via nuclear magneticresonance (MR) imaging, the 2D projection image corresponding to aspecified projection direction, the specified projection directionincluding a path traversing at least a portion of an imaging subject;determine a change between the generated 2D projection image and thereference imaging information; and control delivery of the radiationtherapy at radiation therapy output least in part using the determinedchange between the obtained 2D projection image and the referenceimaging information.

Each of the non-limiting examples described in this document can standon its own, or can be combined in various permutations or combinationswith one or more of the other examples.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In the event of inconsistent usages between this document and anydocuments so incorporated by reference, the usage in this documentcontrols.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In this document, the terms “including” and “inwhich” are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, composition, formulation, or process that includes elements inaddition to those listed after such a term in a claim are still deemedto fall within the scope of that claim. Moreover, in the followingclaims, the terms “first,” “second,” and “third,” etc. are used merelyas labels, and are not intended to impose numerical requirements ontheir objects.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, in an example, the code can be tangiblystored on one or more volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable media can include, but arenot limited to, hard disks, removable magnetic disks, removable opticaldisks (e.g., compact disks and digital video disks), magnetic cassettes,memory cards or sticks, random access memories (RAMs), read onlymemories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to allowthe reader to quickly ascertain the nature of the technical disclosure.It is submitted with the understanding that it will not be used tointerpret or limit the scope or meaning of the claims. Also, in theabove Detailed Description, various features may be grouped together tostreamline the disclosure. This should not be interpreted as intendingthat an unclaimed disclosed feature is essential to any claim. Rather,inventive subject matter may lie in less than all features of aparticular disclosed embodiment. Thus, the following claims are herebyincorporated into the Detailed Description as examples or embodiments,with each claim standing on its own as a separate embodiment, and it iscontemplated that such embodiments can be combined with each other invarious combinations or permutations. The scope of the invention shouldbe determined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

The claimed invention is:
 1. A computer-implemented method comprising: generating, using one or more processors, a plurality of two-dimensional (2D) magnetic resonance (MR) projection image data representing different projection angles; binning, using the one or more processors, the plurality of 2D MR projection image data using information indicative of temporal position within a physiologic cycle; and constructing, using the one or more processors, a three-dimensional (3D) image representation using the binned plurality of 2D MR projection image data.
 2. The computer-implemented method of claim 1 further comprising constructing four-dimensional (4D) imaging information by aggregating 3D image representations including the 3D image representation.
 3. The computer-implemented method of claim 1 further comprising: receiving reference imaging information; determining a change between the generated 3D image representation and the reference imaging information; and generating a therapy protocol for delivery of radiation therapy at least in part using the determined change.
 4. The computer-implemented method of claim 1, wherein generating the plurality of 2D MR projection image data comprises aggregating one-dimensional (1D) projection lines acquired from the MR projection imaging, wherein depth information along a given 1D projection line of the 1D projection lines is compressed into a single pixel value associated with the given 1D projection line.
 5. The computer-implemented method of claim 4, wherein the 1D projection lines are oriented to spatially diverge from one another.
 6. The computer-implemented of claim 1, wherein the projection angles are specified to capture projection directions around an imaging subject.
 7. The computer-implemented of claim 1, wherein constructing the 3D image representation comprises updating a previous 3D image representation with new information.
 8. The computer-implemented of claim 1, wherein binning the plurality of 2D MR projection image data comprises: obtaining a function that represents the physiological cycle as a function of time; determining a portion of time of the function on which a given 2D MR projection image data of the plurality of 2D MR projection image data falls; and associating the given 2D MR projection image data with a bin associated with the determined portion of time.
 9. The computer-implemented of claim 1, wherein binning the plurality of 2D MR projection image data comprises: obtaining a function that represents the physiological cycle as a function of amplitude ranges; determining an amplitude range of the function on which a given 2D MR projection image data of the plurality of 2D MR projection image data falls; and associating the given 2D MR projection image data with a bin associated with the determined amplitude range.
 10. The computer-implemented method of claim 1, wherein generating the plurality of 2D projection image data comprises at least one of acquiring a 2D MR imaging slice perpendicular to a projection angle without requiring a slice selection gradient, or acquiring a 2D MR imaging slice perpendicular to a projection angle using a slice selection gradient defining a slice sufficiently large in depth to encompass an entirety of a radiation therapy target extent in a dimension parallel to the projection angle.
 11. A radiation therapy system, comprising: one or more processors configured to: generate a plurality of two-dimensional (2D) magnetic resonance (MR) projection image data representing different projection angles; bin the plurality of 2D MR projection image data using information indicative of temporal position within a physiologic cycle; and construct a three-dimensional (3D) image representation using the binned plurality of 2D MR projection image data.
 12. The radiation therapy system of claim 11, wherein the one or more processors are further configured to construct four-dimensional (4D) imaging information by aggregating 3D images including the 3D image representation.
 13. The radiation therapy system of claim 11, wherein the one or more processors are further configured to: receive reference imaging information; determine a change between the generated 3D image representation and the reference imaging information; and generate a therapy protocol for delivery of radiation therapy at least in part using the determined change.
 14. The radiation therapy system of claim 11, wherein the one or more processors are further configured to generate the plurality of 2D MR projection images by aggregating one-dimensional (1D) projection lines acquired from the MR projection imaging, wherein depth information along a given 1D projection line of the 1D projection lines is compressed into a single pixel value associated with the given 1D projection line.
 15. The radiation therapy system of claim 11, wherein the projection angles are specified to capture projection directions around an imaging subject.
 16. The radiation therapy system of claim 11, wherein the one or more processors are further configured to bin the plurality of 2D MR projection image data by: obtaining a function that represents the physiological cycle as a function of time; determining a portion of time of the function on which a given 2D MR projection image data of the plurality of 2D MR projection image data falls; and associating the given 2D MR projection image data with a bin associated with the determined portion of time.
 17. The radiation therapy system of claim 11, wherein the one or more processors are further configured to bin the plurality of 2D MR projection image data by: obtaining a function that represents the physiological cycle as a function of amplitude ranges; determining an amplitude range of the function on which a given 2D MR projection image data of the plurality of 2D MR projection image data falls; and associating the given 2D MR projection image data with a bin associated with the determined amplitude range.
 18. A non-transitory computer-readable medium encoded with non-transitory computer-readable instructions for instructing one or more processors to perform operations comprising: generating a plurality of two-dimensional (2D) magnetic resonance (MR) projection image data representing different projection angles; binning the plurality of 2D MR projection image data using information indicative of temporal position within a physiologic cycle; and constructing a three-dimensional (3D) image representation using the binned plurality of 2D MR projection image data.
 19. The non-transitory computer-readable medium of claim 18, wherein binning the plurality of 2D MR projection image data comprises: obtaining a function that represents the physiological cycle as a function of time; determining a portion of time of the function on which a given 2D MR projection image data of the plurality of 2D MR projection image data falls; and associating the given 2D MR projection image data with a bin associated with the determined portion of time.
 20. The non-transitory computer-readable medium of claim 18, wherein binning the plurality of 2D MR projection image data comprises: obtaining a function that represents the physiological cycle as a function of amplitude ranges; determining an amplitude range of the function on which a given 2D MR projection image data of the plurality of 2D MR projection image data falls; and associating the given 2D MR projection image data with a bin associated with the determined amplitude range. 